Angiogenesis promotes tumor growth and metastasis and is an important therapeutic target in the treatment of cancer. Angiogenesis factors activate transcription factors that control endothelial cell proliferation. RUNX2 is a DNA-binding transcription factor that interacts with the TGFb/Smad family of transcriptional modulators to stimulate cell proliferation and tumor progression. RUNX2 also represses the promoter of p21Cip1, a cyclin-dependent kinase inhibitor, inhibits p21Cip1 protein expression, and reduces TGFb-mediated growth inhibition of endothelial cells. We hypothesize that RUNX2 stimulates angiogenesis and endothelial cell proliferation by promoting cell cycle progression through its inhibition of the TGFb1/Smad pathway and repression of p21Cip1 expression. The following specific aims will test this hypothesis. SPECIFIC AIM 1: To establish a role for RUNX2 in stimulating endothelial cell proliferation and promoting angiogenesis in vivo. SPECIFIC AIM 2: To define the requirement for RUNX2 expression and phosphorylation in controlling endothelial cell cycle progression and angiogenesis. SPECIFIC AIM 3: To determine how RUNX2 promotes cell cycle progression and EC proliferation through inhibition of the TGFb1/Smad pathway and/or the cdk inhibitor, p21Cip1. The goals of this proposal are to define how RUNX2 increases endothelial cell proliferation, to determine how RUNX2 regulates cell cycle progression, and to define the interactions of RUNX2 with Smad signaling components, which regulate p21Cip1 expression. Several molecular approaches will be employed, including siRNA-mediated knockdown of RUNX2, the use of RUNX2-inducible cell lines, and cell cycle regulatory activities of RUNX2. Angiogenesis research may uncover new mechanisms regulating blood vessel formation within tumors and could lead to identification of novel anti-tumor agents or improved drug delivery to tumors. Therefore, the development of anti-angiogenic therapeutic agents that inhibit EC proliferation is highly relevant to the NIH mission to improve public health and is a critical approach that may become important in the treatment of cancer. Although not a topic of this proposal, the strategies and treatments discovered in this study may also be relevant for the treatment of other diseases that depend on angiogenesis and cause significant health problems.